Properties window missing?
You are in the 3D view, and only the 3D view. You need to open the properties editor along side of the 3D view.

Move your mouse to the top right corner. The three little hashes in the corner are a button to split and join windows (editors).  What you need to do is click then drag that button to the left.
Now in that new window change it to the properties editor.





Now the reason you got into this situation is because you opened a file that was saved with this view.
To remedy this (instead of changing the view like I described above) you can simply open the file and leave the "Load UI" option unchecked. That will open the file but use the layout from your startup file.